Patent specification EP-A-582 196 was the first to describe a tire comprising a crown surmounted by a tread, a crown reinforcement, two sidewalls and two beads, a carcass reinforcement passing into the two sidewalls and anchored by means for anchoring in the beads, in which the carcass reinforcement comprises at least one circumferential alignment of reinforcing members (referred to as ‘radial’) oriented radially, arranged adjacently and practically parallel to one another, aligned circumferentially in at least one circumferential alignment from the beads towards the sidewalls, and in which the anchoring means of these radial reinforcing members comprise at least one circumferentially oriented reinforcing member (referred to as ‘anchoring reinforcing member’) axially bordering said circumferential alignments of said radial reinforcing members and cooperating with an adjacent portion of the carcass reinforcement by means of an appropriate rubber composition (referred to as ‘anchoring rubber’), of great hardness, in contact with the anchoring reinforcing member and the adjacent lengths of the first radial reinforcing members, and transmitting the forces between the radial reinforcing members and the anchoring reinforcing members.
For the detailed description of such tires, which are referred to as “bead-wire-less” because they do not have a conventional solid bead wire, of a relatively large diameter, around which the carcass reinforcement usually winds, reference may also be made, by way of examples, to patent specifications EP-A-664 231, EP-A-664 232, EP-A-664 233 (or U.S. Pat. No. 5,660,656), WO-A-98/54006 or WO-A-2004/009380.
Although this new tire bottom-zone architecture has yielded excellent results, in particular in terms of endurance, it has however been noted that the great rigidity of the beads could cause difficulties when mounting and/or demounting the tires, in particular during manual operations, this problem being particularly true for tires of large dimensions such as for example heavy-vehicle tires.
It will be recalled here that that the conventional mounting process of a “tubeless” tire on a generally integral rim comprising a hollow base consists of passing part of the first bead over the rim flange and placing this part in the hollow base, then passing the rest of the bead over the flange due to slight ovalisation of the corresponding bead of the tire, and repeating the same operation to pass the second bead over the flange of the rim. The mounting is then terminated by a final stage of inflation to a pressure such that it ensures that the beads are put in position on the seats bearing on the rim flanges; during this last stage, the beads may cross “humps” which form an obstacle to the passage of said beads as far as their respective seats and then prevent the risks of unseating.
To overcome this problem of mounting ability, it was proposed first of all, according to what is taught by patent specification EP-A-751 015 (or U.S. Pat. No. 5,702,548), to use anchoring cables of high non-structural elongation, in particular layered cables of construction (2+7) or (3+8), which have undergone a specific heat treatment. These cables, which are said to be of “high-elongation” type, are characterized, before and after curing of the tire, by a particularly high operational elongation (total of their elastic elongation Ae and of their plastic elongation Ap), greater than 4%. However, such an elongation is obtained at the cost of what is called a recovery annealing heat treatment, carried out at a low temperature of between 250° C. and Ac1 (temperature corresponding to a transformation of the crystalline structure of the steel), which has the disadvantage of being relatively complex and expensive.
To overcome this problem of mounting ability, patent application EP-A-1 277 600 did propose another, more economic, solution, consisting of using a rubber composition of reduced rigidity, having an elasticity modulus of between 10 and 20 MPa at a deformation of 10%, and a high creep resistance due to a specific formulation, as anchoring rubber. It is however noted nowadays that a relatively low rigidity of the anchoring rubber can adversely affect somewhat the road behaviour of vehicles fitted with such tires, in particular under sports running conditions; this is the case in particular for top-of-range passenger vehicles, the user of which wishes to have a very high level of road behaviour, in all circumstances, without compromise on safety, in particular on the grip properties, nor on the life of the tires.
In continuing its research, the Applicant discovered a novel solution which makes it possible to improve existing compromises in terms of mounting ability of the tires and road behaviour, without requiring modification of the architecture of the bottom zone of the bead-wire-less tires.